This is a revised application for funds to purchase a transmission electron microscope. This microscope will be shared by 13 independent investigators currently receiving NIH-funding for projects described in this proposal. These investigators are faculty members in the Departments of Neurology and Pathology. The shared electron microscope will be an integral part of the new Institute of Human Neurosciences and thus will be made available to an even larger group of scientists investigating a variety of clinically relevant problems at Cornell Medical College. The projects in this proposal focus on morphological studies of (1) synaptology and plasticity, (2) localization of the beta adrenergic receptor mRNA, (3) transmitter-specific interactions of mesolimbic and nigrostriatal dopaminergic neurons, (4) cellular interactions between neurons in circumventricular organs, (5) circuitry of the septo-hippocampal pathway that may be implicated in memory dysfunctions, (6) synaptic interactions associated with central control of the circulation through the nuclei of the solitary tracts, rostral ventrolateral medulla, and spinal cord, (7) local neural control of cerebral blood flow and metabolism, and (8) neuropathological changes caused by accumulation of excessive hydrogen ions. The existing electron microscope can not meet the present or projected needs of these projects to do ultrastructural analysis or quantitative measurements. The purchase of a Philips model CM-10 electron microscope or other comparably efficient computer-based instrument would satisfy both the need for increasing availability of an easy-to-use electron microscope and for direct on-line analysis. This microscope would provide for continued progress and significantly improve the efficiency of the research. Proper utilization and sharing of the instrument are ensured by the experienced staff.